Method for densifying surface of powder metallurgy article and apparatus for the same

ABSTRACT

A method of densifying a surface of a powder metallurgy article and an apparatus for the same are provided. A powder metallurgy blank is fixed in position in a fixture for being subjected to a surface treatment that employs an actuating member to exert to a pre-selected surface of the powder metallurgy blank simultaneously a spinning force and a vertically pressing force. The pre-selected surface can thus be densified to have sufficient wear resistance due to the application of the bi-directional forces.

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for surface treatment of a metal article, and more particularly, to a method and apparatus for densifying the surface of a powder metallurgy article.

BACKGROUND OF THE INVENTION

Metal tools or components fabricated by forging or casting technology are well-known to have drawbacks that, the waste of material is considerable which adds to the cost of the product and forging or casting is time-consuming to carry out.

To cope with the aforementioned problems, metal tools or components made of powder metallurgy material have been developed. Such powder metallurgy tools or components, such as bearing rings, can be fabricated in a cost-effective and a time-saving way. However, the powder metallurgy tools or components are of porous structures that make them have mechanical properties inferior to the cast or forged tools or components, especially, for example, the wear resistance. Consequently, densifying the surface of a powder metallurgy tool or component is usually required in order to improve the mechanical properties to a desired level that should be met in industrial application. The conventional method for surface treatment in this art is typically achieved by exerting a roll pressure to the to-be-densified surface of a powder metallurgy tool or component. Examples are U.S. Pat. Nos. 4,059,879 and 5,711,187 or U.S. Patent Application Publication No. 2003/0226386 A1. Such a rolling treatment to the surface is capable of obtaining a structural densification result but still not satisfactory in wear resistance for optimum performance. It is because the rolling treatment can merely provide a unidirectional pressure to the surface, which tends to result in failure in densifying the surface to a desired depth.

SUMMARY OF THE INVENTION

It is accordingly a primary objective of the present invention to provide a method for densifying the surface of a powder metallurgy article and apparatus for the method, which is capable of densifying the surface to a depth greater than the prior art such that wear resistance is improved.

To achieve the above and other objectives, a method for densifying the surface of a powder metallurgy article device is provided. The method comprises the steps of: fixing in position in a fixture a sintered powder metallurgy blank; performing a surface treatment to a pre-selected surface of the sintered powder metallurgy blank, the surface treatment being performed by contacting the pre-selected surface of the sintered powder metallurgy blank with an actuating member that allows at least a vertically pressing force and a spinning force to be simultaneously exerted onto the pre-selected surface of the sintered powder metallurgy black; and removing the thus-obtained powder metallurgy article from the fixture as soon as the pre-selected surface of the powder metallurgy blank has been densified to a predetermined hardness.

The material suitable for use in the actuating member has no specific limitation as long as the actuating member has a hardness greater than the powder metallurgy article. However, tool steel, high speed steel and tungsten carbide are preferred materials.

The spinning speed, moving speed for driving the actuating member over the surface to be densified and vertical pressing force of the actuating member are the factors which affect the density and depth of the surface to be densified. That is, those factors are variable depending on the requirements of wear resistance for a powder metallurgy article.

The contact surface of the actuating member can be planar or non-planar, depending upon the surface of a powder metallurgy article to be densified.

The powder metallurgy blank may be formed by pressurizing and sintering a porous powder metallurgy material. The sintered powder metallurgy blank has a density of about 80 to 90% of that of an actual steel.

The present invention also provides an apparatus for densifying a surface of a powder metallurgy article which comprises a fixture for fixing a powder metallurgy blank in position; an actuating member driven by a driving unit for exerting at least a vertically pressing force and a spinning force simultaneously onto a pre-selected surface of the powder metallurgy blank; a control unit for controlling the driving unit to drive the actuating member with predetermined conditions; and a power source for supplying power to the driving unit and the control unit.

The actuating member has a contact surface for the actuating member to have a direct contact with the pre-selected surface of the powder metallurgy blank. The contact surface can further provide the pre-selected surface with a friction force so as to enhance the densification of the pre-selected surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:

FIG. 1 is a schematic view of the apparatus according to the present invention;

FIG. 2 is a schematic view of the method according to the present invention; and

FIG. 3 is a cross-section view of the powder metallurgy article with a densified surface obtained by using the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the apparatus according to the present invention is essentially consisted of a fixture 1 for a powder metallurgy blank 6 to be firmly fixed thereon, an actuating member 2, a driving unit 3 for driving the actuating member 2 to exert onto a pre-selected surface 60 of the powder metallurgy blank 6 simultaneously a vertically pressing force (indicated by downwardly pointing arrows) and a spinning force (indicated by a curving arrow), a control unit 4 for controlling the driving unit 3 to drive the actuating member 2 with predetermined conditions, and a power source 5 for supplying power to the driving unit 3 and the control unit 4.

The fixture 1 is capable of securely fixing in position the powder metallurgy blank 6 for surface treatment via clamping or securing means which are not shown in the drawings, as such clamping or securing means are conventional for persons skilled in the pertinent art.

The actuating member 2 is suitably in the form of a rod provided with a contact surface 20, so as for the actuating member 2 to have a direct contact with the pre-selected surface 60 of the powder metallurgy blank 6 via the contact surface 20. The actuating member 2 is driven by the driving unit 3 to move horizontally across over the entire pre-selected surface 60, while driven to spin around the axis of the actuating member 2 and to synchronously press downwardly against the pre-selected surface 60. By way of the spinning and downward pressure provided by the actuating member 2, the pre-selected surface 60 of the powder metallurgy blank 6 can be sufficiently densified to obtain desired wear resistance for optimum performance. The contact surface 20 of the actuating member 2 can be further treated to provide the pre-selected surface 60 of the powder metallurgy blank 6 with a friction force, so as to intensify the densification effect.

The control unit 4 is used for setting the operating conditions for controlling the driving unit 3 to drive the actuating member 2. The operating conditions for the actuating member 2, such as the spinning speed, the moving speed and/or magnitude of the vertically pressing force, can produce a direct impact on the density and the densification depth of the surface of the powder metallurgy article. Therefore, the operating conditions for controlling the driving unit are to be adjusted based on the requirements for the density and densification depth of a surface of a powder metallurgy article as well as the material of the powder metallurgy article.

The driving unit 3 should include transmission mechanisms for horizontally moving the actuating member 2 above the powder metallurgy blank 6, spinning the actuating member 2 to generate a spinning force onto the pre-selected surface 60, and descending the actuating member 2 to produce a vertically pressing force against the pre-selected surface 60. Since the design of the transmission mechanisms for the driving unit 3 can adopt any suitable conventional technologies and should be evident to persons in the pertinent art, detailed description thereto will be eliminated here for purposes of simplification.

To implement the method according to the present invention, please refer to FIG. 2.

First, in step S1, a powder metallurgy blank 6 was made from a commercially available powder metallurgy material, MPIF standard 35 FLNC 4405, having a formation density of 6.8 g/cm³, a surface hardness (HRA) of 55, and a composition of 0.4 to 0.7% of C, 1.0 to 3.0% of Ni, 0.65 to 0.95% of Mo, 1.0 to 3.0% of Cu, and Fe. The powder metallurgy blank 6 was placed on the fixture 1 for fixation in position.

Then, in step S2, the actuating member 2 was driven by the driving unit 3 powered by the power source 5 to have contact with the pre-selected surface 60 of the powder metallurgy blank 6 via the contact surface 20. The actuating member 2, when in position, was operated to exert simultaneously a spinning force and a vertically pressing force onto the pre-selected surface 60 for surface densification. It should be noted that the movement, spinning speed, moving speed, and magnitude of the vertically pressing force of the actuating member 2 was controlled by the control unit 4 via the driving unit 3. Finally, in step S3, when the surface treatment as described in the previous step completed, the thus-obtained powder metallurgy article was removed from the fixture 1. The thus-obtained powder metallurgy article has a densified surface layer of thickness up to 1.0 mm, as shown in FIG. 3, and a HRA of 72.

The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A method for densifying surface of a powder metallurgy article, comprising the steps of: fixing in position in a fixture a powder metallurgy blank; performing a surface treatment to a pre-selected surface of the powder metallurgy blank, wherein the surface treatment is performed by contacting the pre-selected surface of the powder metallurgy blank with an actuating member that allows at least a vertically pressing force and a spinning force to be simultaneously exerted onto the pre-selected surface of the powder metallurgy blank; and removing the powder metallurgy article thus-obtained from the fixture as soon as the pre-selected surface of the powder metallurgy blank has been densified to a predetermined hardness.
 2. The method of claim 1, wherein the powder metallurgy blank is formed by pressurizing and sintering a porous powder metallurgy material.
 3. The method of claim 1, wherein the actuating member is made of a material with hardness greater the powder metallurgy blank.
 4. The method of claim 1, wherein the actuating member is movable relative to the pre-selected surface of the powder metallurgy blank.
 5. The method of claim 4, wherein the moving range of the actuating member is designed to cover the entire pre-selected surface of the powder metallurgy blank.
 6. The method of claim 1, wherein the actuating member exerts simultaneously the at least a vertically pressing force and a spinning force to the pre-selected surface of the powder metallurgy blank via a contact surface thereof.
 7. The method of claim 6, wherein the contact surface of the actuating member can further provide a friction force to the pre-selected surface of the powder metallurgy blank.
 8. An apparatus for use in the method of claim 1, comprising: a fixture for fixing in position a powder metallurgy blank; a driving unit; an actuating member driven by the driving unit for exerting at least a vertically pressing force and a spinning force simultaneously onto a pre-selected surface of the powder metallurgy blank; a control unit for controlling the driving unit to drive the actuating member with predetermined conditions, so as to densify the pre-selected surface of the powder metallurgy blank to reach a desired hardness; and a power source for supplying power to the driving unit and the control unit.
 9. The apparatus of claim 8, wherein the driving unit can further drive the actuating member to move all over the entire pre-selected surface of the powder metallurgy blank.
 10. The apparatus of claim 8, wherein the predetermined conditions at least comprise a spinning speed, a moving speed, and the vertically pressing force of the actuating member driven by the driving unit.
 11. The apparatus of claim 8, wherein the actuating member exerts simultaneously the at least a vertically pressing force and a spinning force to the pre-selected surface of the powder metallurgy blank via a contact surface thereof.
 12. The apparatus of claim 11, wherein the contact surface of the actuating member can further provide a friction force to the pre-selected surface of the powder metallurgy blank.
 13. The apparatus of claim 8, wherein the actuating member is made of a material with hardness greater than the powder metallurgy blank.
 14. The apparatus of claim 8, wherein the powder metallurgy blank is formed by pressurizing and sintering a porous powder metallurgy material. 